1. Field of the Invention
The present invention relates to a method for selectively etching an organic film for a plating resist and so on.
2. Description of the Background Art
In the course of manufacturing electronic components or the like, a process of applying an organic film such as a plating resist to a substrate and selectively etching the organic film may be performed. In this process, the surface of the organic film is partially protected by a hard mask layer made of SiO2 or the like, and thereafter, dry etching is performed to remove portions of the organic film which are exposed from the hard mask.
As an example of the organic film etching method, a method of isotropically etching an organic film by using oxygen radicals has been known. This method is characterized by its high etching rate for the organic film.
As another method, a method of anisotropically etching an organic film by using an etching gas obtained by mixing CH-based gas and NH3 gas has been known (JP-A-2005-79192). In this method, during the etching, the organic film and the etching gas chemically react with each other to form a protective film on side surfaces of the organic film. Therefore, the etching can be performed with the side surfaces being protected, and thereby the pattern of the hard mask layer can be accurately transferred onto the organic film.
However, the etching method using oxygen radicals has the following drawback. That is, since this etching is isotropic etching although the etching rate is high, if, for example, the organic film is thick, it is difficult to accurately transfer the pattern of the hard mask layer onto the organic film. For example, when a wiring pattern is formed on a substrate having a large height difference of several μm or more, the thickness of the organic film (plating resist) needs to be increased. Since the isotropic etching advances also on side walls, if the organic film is thick, it is difficult to accurately transfer the pattern of the hard mask layer onto the organic film. In particular, when a fine wiring pattern needs to be formed on the thick organic film, it is difficult for the isotropic etching to accurately transfer the fine pattern of the hard mask layer onto the organic film.
In addition, the method of anisotropically etching an organic film by using the etching gas obtained by mixing CH-based gas and NH3 gas allows accurate transfer of the pattern of the hard mask layer onto the organic film. However, this etching method has the following drawback. That is, when the thickness of the organic film needs to be increased as described above, the etching takes a long time since the etching rate is low. Therefore, these etching gases are hard to be used.
The present invention has been made in view of the above background, and provides a method for etching an organic film which allows accurate transfer of the pattern of a hard mask layer at a high etching rate, which enables etching in a short time, even in etching of a thick organic film as in the case of etching an organic film formed on a substrate having a large height difference.